Silver halide photographic materials are formed by introducing various photographically useful compounds into hydrophilic colloid layers in order to allow various photographic functions to be exhibited. In that case, in particular, with respect to multi-layer photographic materials, water-insoluble substances are used to hold intended photographically useful substances in particular layers, to allow their functions to be exhibited. These water-insoluble substances are oil-soluble substances in many cases. The water-insoluble substance is formed into fine emulsified particles by stirring it at a high speed, with a dispersing solvent, a dispersing medium, and, if required, a co-solvent (high-boiling organic solvent), in the presence of a surface-active agent, in order to introduce the water-insoluble substance into a hydrophilic colloid layer of a photographic material, followed by coating and drying.
Obtaining a dispersion that is stable during storage and during the coating step and the drying step is required in order to avoid problems, such as nibs; and obtaining or not obtaining finely dispersed grains, influence the photographic properties greatly. For example, it is known that, in dispersing dye-forming couplers (hereinafter abbreviated to couplers), obtaining a fine dispersion can improve reactivity and can attain a high dye-forming efficiency; and, in dispersing a color-mix inhibitor for use in an intermediate layer, obtaining a fine dispersion can secure a high color-mix inhibition activity.
Further, in the case of nucleators, which are water-insoluble photographically useful substances for use, for example, in photographic materials for printing, since the polarity of nucleators is subtle, there are few preferable dispersion techniques. A dispersion is prepared, for example, by mixing a solution of a nucleator in an organic solvent in the presence of large amounts of a surface-active agent and a protective colloid, followed by deposition, which technique involves a problem in view of the stability of the dispersion and the use of a large amount of a surface-active agent.
In the above production of a fine particle dispersion, generally, since the type and the amount of the used surface-active agent cause the size and stability of the obtainable grains to change greatly, the surface-active agent is a great governing factor in the emulsifying and dispersing processes. Therefore, research on surface-active agents that will enable the fine dispersion has hitherto been made, and various emulsion stabilizers useful for photographic systems have been found. Examples of these emulsion stabilizers are described, for example, in JP-A ("JP-A" means unexamined published Japanese patent application) Nos. 129229/1976 and 20251/1985, U.S. Pat. Nos. 3,428,456 and 3,963,688, and West German Patent Application (OLS) Nos. 1,932,299 and 2,123,455. However, there are as yet no surface-active agents that can give stable fine dispersions when they are used in small amounts for a wide variety of compounds. Although use of a large amount of a surface-active agent and use of a water-miscible organic co-solvent can give a fine dispersion, use of a large amount of a surface-active agent results in processing stain and foaming, due to the dissolving out thereof into a photographic processing solution in a processing step and accumulation thereof in the photographic processing solution, often resulting in serious problems. Particularly, in recent years, as the replenishment rate of processing solutions has been made low, even the conventional amount of surface-active agents to be used sometimes causes a problem. Further, since the use of a water-miscible organic solvent is accompanied by the generation of organic solvent gas when the dispersion is produced, a serious problem occurs in view of the need for counterplan equipment for the recovering process and the deterioration of the production environment.
Therefore, development of a surface-active agent that, when used in a small amount for a wide variety of compounds, can give stably a fine dispersion, is desired.
As described above, in producing a fine dispersion for photographic materials, high-boiling organic solvents are often used. If a dispersion is prepared without using these high-boiling organic solvents, particles of the dispersion are difficult to be made fine stably. In addition, problems often arise, i.e., the photographic properties of the photographic material coated with the dispersion are damaged (e.g., the sensitivity is lowered, the color-forming property is lowered, or fine crystals deposit), which is a very great hindrance to the designing of photographic materials. On the other hand, however, injurious effects occur due to the use of high-boiling organic solvents. For example, it is well known that when a dye-forming coupler is used as an oil-soluble photographically useful substance, stain occurs on the surface of the photographic material, due to exudation of the high-boiling organic solvent with the lapse of time during storage of the photographic material. Further, an increase in the film thickness of the photographic material, resulting from an increase in a hydrophilic colloid used to compensate for softening of the film, caused by the introduction of the oil-soluble component; and lowering of the color-forming property, due to lowering of the reactivity of a coupler, caused by crystallization of the coupler, cause serious problems.
Therefore, development of a technique capable of preparing a fine dispersion without damaging the reactivity of the dispersed oil-soluble photographically useful compound, and without using a high-boiling organic solvent, is desired.
The above dispersion prepared for photographic materials is stored in a refrigerator or at ordinary temperatures, according to requirement, after the preparation and before the production of the photographic material. At that time, the proceeding of deterioration of the dispersion with the lapse of time, such as separation of oil components and crystallization, often causes a serious problem. In this case, since the stability after the lapse of time changes due to the type and amount of the surface-active agent used, development of a surface-active agent that is excellent in stability during storage of the dispersion is desired.